The present invention relates to thin three-dimensional flexible adhesive film structures that exhibit minimal or no tack under normal handling conditions, but which adhere to a wide variety of substrates when pressure is applied.
Sheet-like materials for use in the containment and protection of various items, as well as for the preservation of perishable materials such as food items, are well known in the art. Such materials can be utilized to wrap items individually and can be utilized to form a cover or seal for a semi-enclosed container. One class of such materials in common use today comprises those of a polymeric composition formed into a thin, conformable web commonly supplied in rolled form. Common examples of such materials are polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and polyethylene (PE) sheet materials. These materials exhibit a clinging character on at least one surface due to the properties of the polymeric materials from which they are formed, and/or due to the presence of additives such as plasticizers, tackifiers, etc. When these film materials are folded or wrapped around in items, they cling either to the item or to themselves, or both. The barrier properties of many such materials, particularly their oxygen, moisture/moisture vapor, and odor barrier properties, provide the desired preservation characteristics for perishable items such as food items and/or items which oxidize or otherwise degrade more rapidly with continued exposure to environmental conditions.
While these materials have achieved a certain level of acceptance, difficulties often are encountered in locating or isolating the end portion of the material when it is supplied in the form of a continuous roll in a dispensing carton or apparatus. In addition, the tendancy of these film materials to cling to themselves also increases the dispensing force required to unroll the web, and often leads to undesirable and premature clinging of a sheet of the material to itself before it can be wrapped around an item. Also, because these materials xe2x80x9cclingxe2x80x9d to themselves and other surfaces, i.e., they exhibit an attraction or affinity for the material rather than form an adhesive bond, their affinity for a complementary surface is highly dependent upon material characteristics such as chemical composition, electrical conductivity, surface energy, surface finish, etc.
The problem of premature adhesion also has been recognized in the art of tapes, labels, and other articles using pressure sensitive adhesives to adhere an adhesive coated surface to a substrate. For example, before the adhesive coated surface can be properly positioned over a substrate, inadvertent contact of the adhesive with the substrate or target causes premature adhesion at one or more locations thereby inhibiting proper positioning.
Various procedures and products have been suggested in the prior art for overcoming the problem of premature adhesion of adhesive articles to substrates. U.S. Pat. No. 5,662,758 (Hamilton et al), for example, describes a method for making a flexible film having pressure sensitive adhesive protected from inadvertent adheranc e. The method coats a forming screen with an interconnected layer of pressure sensitive adhesive and places a piece of flexible film in contact with the layer of adhesive. The layer of adhesive preferentially adheres to the piece of flexible film. The forming screen has a plurality of recesses therein, and the coating step applies a layer of adhesive without bridging the recesses. Another step forms the piece of flexible film to create a plurality of protrusions extending into the recesses. Since contact of the adhesive with a target surface is prevented by the outer most ends of the protrusions, there is no adhesion between the three-dimensional sheet and the target surface until pressure is applied to the non-adhesive side of the flexible film whereby the adhesive within the recesses comes in contact with the target surface and the film adheres to the target surface.
U.S. Pat. No. 5,968,633 (Hamilton et al) describes a selectively-activatable sheet material for dispensing and dispersing a substrate onto a target surface wherein the sheet material comprises (a) a three-dimensional sheet of material having a first side and a second side, said first side having a plurality of hollow protrusions extending outwardly therefrom and separated from one another from valleys, said second side having a plurality of depressions corresponding with said plurality of hollow protrusions; and (b) a substance adhering to and partially filling a location protected from external contact comprising at least one of said valleys and said depressions, such that said sheet material may be selectively activated by deforming said hollow protrusions to deliver said substance to a target surface. The substances which may be included in the recesses of the selectively-activatable sheet include cleansing agents, medicinal agents, emollients, lubricants, adhesives, fragrances, deodorants, etc.
It has also been suggested in the prior art that the problem of premature adhesion can be overcome by providing standoffs on a material surface between which adhesive elements are located. Standoffs include any means extending outwardly from an adhesive surface which is contacted first before the adhesive surface is exposed to contact by another surface. Protecting an adhesive from premature contact by another surface also has been achieved by adding strips of polymer foam to form deformable standoffs on an adhesive surface. Polymer foams, however, tend to spring back and exert a peel force on the adhesive bond to the target surface.
U.S. Pat. No. 5,141,790 (Calhoun et al), discloses a repositional pressure sensitive tape with an adhesive coated surface which has clumps of particles spaced out on the adhesive to keep the adhesive from touching the target surface until the sheet is pressed against the target surface. The particles are smaller than the thickness of the adhesive layer so that when pressed, the particles sink below the surface of the adhesive and no longer provide their spacing function.
U.S. Pat. No. 5,871,607 (Hamilton et al) describes a material having a substance protected by deformable standoffs, and the method of making the material. In particular, the patent describes a method for making a three-dimensional structure having outermost surface features and having spaces for containing a substance internal to said outermost surface features such that said substances protected from inadvertent contact with external surfaces. The method comprises the steps of coating a substance onto a forming surface, applying a piece of material to the substance coated forming surface, transferring said substance from said forming surface to said piece of material, and forming said piece of material into a three-dimensional structure on said forming surface while said substance is in contact with said forming surface in order to accurately register the three-dimensional structure with said substance.
International application WO 97/25256 relates to improved storage wrap materials which comprise a sheet of material having a first side and a second side. The first side comprises an active side exhibiting an adhesion peel force after activation by a user which is greater than the adhesion peel force exhibited prior to activation by a user. The storage wrap material may be activated by different approaches, but in a preferred embodiment, the active side is activatable by an externally applied force exerted upon the sheet of material. The storage wrap material is selectively activatable by a user in discrete regions to provide adhesive properties where and when desired. The use of an adhesive or adhesive-like substance on the surface of the material provides an adhesion peel force after activation which is sufficient to form a barrier seal against a target surface at least as great as those of the material and the target surface such that perishable items, such as food items, may be effectively preserved.
A three-dimensional flexible adhesive film structure is described which comprises:
(A) a flexible polymer face film having a front surface and a back surface, said front surface comprising at least one area having one or more, three-dimensional hollow protrusions extending outwardly from said front surface, the back surface of the face film comprising at least one area having one or more three-dimensional spaced depressions corresponding to said one or more hollow protrusions on the front surface of the face film,
(B) an adhesive layer having a front surface and a back surface wherein the front surface of the adhesive layer is in contact with and adhered to the back surface of the flexible polymer face film, and
(C) a patterned layer of a non-adhesive material having a front surface and a back surface and containing one or more areas free of non-adhesive material wherein the front surface of the layer of non-adhesive material is in contact with and adhered to the back surface of the adhesive layer, and the area or areas free of non-adhesive material are within the three-dimensional depression or depressions in the back surface of the face film.
The flexible adhesive film structures of the invention exhibit tack on demand characteristics. Thus, the film is capable of showing minimal or no tack under normal handling conditions, but when pressed against a target surface, exhibits the desired adhesion. When the film is removed from the target surface, little or no adhesive is left on the substrate leaving a clean surface.